It is highly desirable to have available in an A.C. rotating generator system a means for effecting good control or regulation of the A.C. voltage output thereof over a wide range of voltages with very low dissipated power losses due to the voltage control or regulating means therefor. It also would be desirable that the voltage control operate rapidly, and particularly that the regulation or control be effective in a period of the order of one cycle, whereby to attain or maintain a selected voltage.
While many expedients and techniques are known for regulating and controlling the voltage of an A.C. generator, substantially all such known expedients or techniques incur significant power losses or power dissipation. Further, in many such voltage control systems the controls operate relatively slowly, so that many cycles of A.C. of incorrect voltage are generated before the A.C. voltage reaches the desired value.
For many applications in laboratories, industry, military and government, it is desirable to have available a supply of A.C. power at a specified substantially constant voltage and at a substantially constant selected frequency. Public utility power systems are characterized by many voltage irregularities and faults as well as complete power interruptions which may extend from a few cycles to several hours or longer. It is common for substantial voltage drops to occur in utility lines, often at certain times of the day, with 10% variations in voltage being normal from the low to the high values of A.C. line input to homes and business establishments. In an article entitled "Focus on Uninterruptible Power Supplies and Inverters" appearing in part on pages 100 and 101 of the May 10, 1975 issue of "Electronic Design," there are listed the types and frequency of occurrence of many of these public utility irregularities and faults. In an article on pages 38 to 45 of the July 1977 issue of "Mini-Micro Systems" entitled "Power Protection Equipment: A Survey" by Kenneth G. Brill, some details of the nature and frequency of utility power problems are set forth and their effect on computer operation. This article also lists the protection alternatives available to secure constant voltage A.C. as well as other desirable characteristics of power sources, particularly for computers.
Numerous other electronically controlled apparatus, other than computers, requires A.C. power of a relatively constant frequency and a relatively constant selected voltage in order to function properly. If either the frequency or the voltage, or both, depart from prescribed limits, many machines, apparatus, and control equipment in factories, laboratories, hospitals, military installations, communications such as radio, television and telephony, and the like, can malfunction or misfunction with consequential losses, interruptions of processes and procedures, physical damage and dangerous conditions occurring.